1. Field of the Invention
This invention relates to machine tools and more particularly to turret punch presses.
2. Prior Art
Turret punch machines are normally equipped with upper and lower rotatable turret assemblies. Each assembly can generally be considered as consisting of a centrally mounted rotatable disc which has one or more ring-like areas adjacent its outer periphery in which tools are positioned. A normal turret punch press will have the upper turret disc, or table, carry a plurality of punches and the lower turret disc, or table, carry a plurality of dies.
It is common for both turret tables to be machined, the upper turret being machined with a plurality of openings extending axially therethrough in the ring area each of which opening individually receives one punch. The punch is generally one part of an assembly which may include the punch body itself, springs for returning the punch to a predetermined position, punch holder mechanisms, stripper mechanisms, stripper springs, etc. In its simplest form, the punch assembly is merely positioned in a hole in the turret. In more complex forms, the turret holes may be equipped with guide bushings for guiding the punch or its surrounding stripper and the turret may be further equipped with anchoring means, punch lifting devices, etc, each requiring specific machining of the table.
The die turret table is likewise a machined table and includes a plurality of axially extending openings in the ring area which serve as discharge openings for disposal of punched material. Means are then provided for mounting dies on the lower turret in the area of the machined openings. In a simplier form, the discharge openings may be counterbored adjacent one axial end and the dies may be seated in the counterbore. In more complex embodiments, the dies are carried in die holders which may be of two or more parts and which in turn are mounted on the turret table by means, such as bolts or the like, which require further machining of the lower turret table.
In addition, both turret tables will be equipped or provided with shot pin openings so that reciprocatably movable shot pins can be inserted into table shot pin openings to insure positive precise location of the tools carried by the table as well as a positive location of the tables with respect to one another.
Further, once it has been determined to create a two table turret punching machine, criticality of alignment of the machined openings in the upper turret table with machined openings in the lower turret table demands the application of extremely complex and cumbersome machining and assembly procedures. It is therefore clear that a large part of the expense of manufacturing turret punch presses is involved in the design, manufacture, and assembly of the turret tables which, when completed represent a substantial portion of the bulk of the machine.
Because the turret tables are difficult to manufacture and expensive, they are not generally considered to be a changeable part of the overall machine. Further because of their expense, they are produced in only a relatively small number of configurations. Thus the positioning of the various openings in a turret table is, for all practical purposes, set at the time of manufacture of the table. This has the effect of limiting the versatility of use of the overall punch press and requires that the purchaser pre-select from among the configurations of the turret tables offered and thereafter be limited to working with his choice. Since the versatility of the overall machine is then specified within a range which is a function of the turret table configuration chosen, the presently existing turret punch presses have inherent limitations restricting their overall versatility and applicability. Although it has been suggested to provide a device allowing placement of two small tools at turret positions which normally receive one large tool, see U.S. Pat. No. 3,951,026, nothing has been done to allow changing of turret configuration.
Another disadvantage of the prior art turret punch presses is in the area of tool changing. Tool changing is both restricted and time consuming. First, the variety of tools that can be provided on any turret is restricted by the configuration of that turret. It is not possible to put larger punches or dies in smaller openings. It is expensive, uneconomical and unaccurate to put smaller punches and dies in larger holes. Not only does this later situation require the use of bulky machined pieces to take up the clearance space, it introduces yet another set of interfaces having critical positioning requirements in order to assure that each punch is properly aligned with an associated die.
Further, tool changing requires a great deal of machine down time. In order to insure proper alignment of the punches with the upper turret, the upper turret opening may have a guide bushing formed as a part of the opening wall. If this is the case, then it is practically impossible to change punch body sizes or die holder sizes for any given opening and tool changing is limited to the replacement of punch tips and the replacement of the die. Even this simple change can become cumbersome in those instances where the associated punch assembly portions are carried by the turret. In other types of upper turrets where the majority of the punch assembly is self-contained in a punch housing which merely fits in a given opening, it is easier to change punch size to allow the use of a smaller punch in a larger turret opening. However changing punches in this type of a construction generally requires, at the least, removal of a number of bolts or the like.
Die changing is equally complex. Where the die holder is formed as a part of or is semi-permanently affixed to the lower table, it may be practically impossible to change die size for a given die opening. If not impossible, it requires the removal of portions of the die holder which are normally permanently affixed to the turret, thereby requiring complex realignment procedures when a new die holder is fastened to the turret. Even the relatively simple step of changing a broken or worn die with an equally sized die represents a complex problem requiring the removal of bolts and other die holder portions, all of which can result in substantial machine down time. Because of this, it is not considered to be a part of the standard operating cycle of presently existing turret punch presses to change over die sizes and varieties for relatively small production runs.
It would therefore be a definite advance in the art to provide a turret punch press wherein tool changing is facilitated and the down time necessary to accomplish tool change is reduced. It would further be a major advance in the art to provide a turret punch press overcoming the above described turret configuration limitations.